Method for controlling an artificial orthotic or prosthetic kneejoint

ABSTRACT

A method for controlling an artificial orthotic or prosthetic knee joint, on which a lower-leg component is arranged and with which a resistance device is associated, the bending resistance (R) of which resistance device is changed in dependence on sensor data that are determined by means of at least one sensor during the use of the orthotic or prosthetic knee joint, wherein a linear acceleration (a F ) of the lower-leg component is determined, the determined linear acceleration (a F ) is compared with at least one threshold value, and, if a threshold value of the linear acceleration (a F ) of the lower-leg component is reached, the bending resistance (R) is changed.

The invention relates to a method for controlling an artificial orthoticor prosthetic knee joint, on which a below-knee component is arrangedand which is assigned a resistance device in which the flexionresistance is changed in accordance with sensor data that are determinedvia at least one sensor during the use of the orthotic or prostheticknee joint.

Prosthetic or orthotic knee joints replace or support the function of anatural knee joint. In order to achieve a maximally optimalfunctionality of the artificial knee joint, there are many designs onthe market which influence the behavior of the knee joints during thestance phase and the swing phase. Mechatronic knee joints are known, inwhich the movement situations are detected via a plurality of differentsensors and the sensor data are used to control a resistance device viawhich the flexion resistance or the extension resistance is varied. Onebasic problem is that the great variety of the possible movementsituations can be encompassed only with difficulty in simple rules.Therefore, in order to control actuators and brakes, so-called statemachines are used, which are highly complex and represent many differentactivities. Disadvantages with this are the long development time andthe use of elaborate components.

EP 1 237 513 B1 relates to a supporting device which replaces theexistence or function of a limb and which consists of at least twoparts, connected to each other by an artificial joint, and a controldevice. The supporting device comprises a sensor, which detects aninclination angle relative to a line of gravity of a part connected tothe joint and is coupled to the control device. The control device isarranged in such a way that it influences the joint on the basis ofinclination angle data communicated by the sensor. In one configuration,the inclination angle sensor is arranged as a prosthetic knee joint on athigh tube; in order to enhance the data situation, a second sensor canbe arranged on the lower leg.

DE 10 2008 027 639 A1 relates to an orthotic joint for supporting ananatomical knee joint, having an upper joint part and a lower joint partwhich are connected to each other in an articulated manner. A lockingelement for automatically unlocking and locking the orthotic joint in anarbitrary position is provided, likewise an actuation element for thelocking element and a sensor means for detecting relevant informationfor the unlocking and locking. An evaluation unit for evaluating theinformation acquired, and for forwarding this information to a controland/or regulating unit for the actuation element, is likewise present.The sensor means comprises at least two sensors from the group includinginclination sensors, rotation angle sensors, acceleration sensors orgyroscopes, for acquiring information describing the movement stateand/or resting state of a person. Two sensors of one type or one sensoreach of different types may be selected. All the sensors are arrangeddownward from the anatomical joint, in particular knee joint.

The object of the present invention is to make available a method forcontrolling an artificial orthotic or prosthetic knee joint, with whichmethod a reliable gait pattern can be achieved with minimal outlay incontrol terms.

According to the invention, this object is achieved by a method havingthe features of the main claim.

Advantageous embodiments and refinements of the invention are disclosedin the dependent claims, the description and the figures.

In the method for controlling an artificial orthotic or prosthetic kneejoint on which a below-knee component is arranged and which is assigneda resistance device in which the flexion resistance is modified inaccordance with sensor data that are determined via at least one sensorduring the use of the orthotic or prosthetic knee joint, provision ismade that a linear acceleration of the below-knee component isdetermined, and, if a limit value of a linear acceleration of thebelow-knee component is not reached, the flexion resistance is changed,in particular reduced. With the proposed method, it is possible for aknee joint, by which are understood both orthotic knee joints and alsoprosthetic knee joints, to be controlled exclusively by simple sensors,without elaborate and delicate force measurements having to be carriedout. In particular, the use of DMS applications is thereby maderedundant.

In a development of the invention, provision is made that an extendedstride position of a prosthesis or orthosis with a prosthetic ororthotic knee joint is determined and, when the extended stride positionis present, the flexion resistance is reduced. The extended strideposition is present when the knee angle is 0° or the knee joint isminimally bent, i.e. has a flexion angle within a range of ±5°. If theextended stride position is present, it can be assumed that the user ofthe knee joint is in the terminal stance phase, and therefore areduction in resistance can take place.

In order to detect a terminal stance phase, an absolute angle of thebelow-knee component can additionally be determined, and, if apredefined limit value for the absolute angle of the below-kneecomponent is exceeded, the flexion resistance can be reduced. From theinclination angle of the below-knee component with respect to thevertical, meaningful conclusions can be drawn concerning the particularphase within a stride, such that the absolute angle is a good indicatorof the change, in particular the reduction, of the flexion resistance.

The absolute angle of the below-knee component can be determined from anabsolute angle of a thigh component and from a known, e.g. measured,knee angle or can be measured directly with an inertial angle sensor,which is secured on the below-knee component.

Moreover, provision can be made that the knee angle is additionallydetermined via a knee angle sensor, and, if a limit value for the kneeangle is not reached, the flexion resistance is reduced, since the kneeangle is an indicator of the state of extension of the leg or of theprosthesis and, consequently, of the particular phase within a stepcycle. The knee angle can also be determined from the inertial angles ofthe thigh and of the lower leg.

If several parameters are available, for example the exceeding of alimit value for the absolute angle of the below-knee component, thefalling below a limit value for the knee angle and the falling below alimit value of an acceleration of the below-knee component, it can bemore safely assumed that the flexion resistance is intended to bechanged, in particular reduced, in order to allow a swing phase to beenabled. With the proposed method, it is possible to safely control aknee joint exclusively via simple sensors.

The majority of microprocessor-controlled prosthetic and orthoticsystems are controlled by measurements of force and moment being carriedout by means of strain gauges, the decisive aspect for the safety of aknee joint being the change from a high flexion resistance in the stancephase to a low flexion resistance during the swing phase and vice versa.The change-over is also referred to as enablement of the swing phase. Inaddition to the calculation of bending moments at the ankle level or ofthe knee moment, threshold values of the values calculated from thestrain gauges have to be exceeded in order to enable the swing phase.Furthermore, the enablement of the swing phase often takes place onlyafter a certain forward inclination, such that walking with small stepsbecomes difficult.

In the method according to the invention, the knee joint is controlledexclusively by knee angle sensors and inertial sensors from whose datathe necessary parameters or auxiliary values can be calculated. Theabsolute angle of the below-knee component, i.e. the inclination of thelongitudinal extent of the below-knee component with respect to thevertical, is determined via the inertial sensor. The absolute angle mustexceed a minimum value in order to detect a forward inclination of thebelow-knee component, i.e. an inclination in the walking forwarddirection. Only at a certain angle in forward inclination can it beassumed that a step in the forward direction is to be taken. The kneeangle is determined via a knee angle sensor. If a limit value for a kneeangle is not reached, this is a sign that the user is in a terminalstance phase, such that an enablement of the swing phase and therefore areduction of the flexion resistance are indicated. In addition, theacceleration of the below-knee component is determined. If anacceleration limit value is not reached, it can be assumed that the footcomponent, for example the foot plate or the prosthetic foot, is stilllocated on the ground, and it is therefore ascertained that the patientis in the terminal stance phase of a stride and the flexion resistancecan thus be reduced.

In a development of the invention, provision is made that the knee anglevelocity is determined, and the flexion resistance is reduced only whena limit value for the knee angle velocity is exceeded. A minimum kneeangle velocity should be present, since otherwise a stance situation mayarise in which a reduction of the flexion resistance may be undesired.With the low or relatively low knee angle velocity, it is additionallyensured that the patient is in the terminal stance phase during aforward movement.

An angular velocity of the below-knee component can be calculated or canbe detected via a sensor, for example from the sensor data of agyroscope. The calculated or detected value of the angular velocity iscompared with a limit value, and the flexion resistance is reduced onlywhen the angular velocity is below a limit value.

The linear acceleration of the below-knee component is advantageouslydetermined or measured at the sole level and is used as a basis for thecontrol; the acceleration at the sole level derives from the linearaccelerations at the position of the acceleration sensor, for examplebelow the knee joint axis, the angular acceleration of the below-kneecomponent as a first-order derivative of a gyroscope signal, and thelocation vector of the position of the acceleration sensor to thereference position on the foot, for example on the forefoot. From thelinear accelerations at the sole level, conclusions are drawn concerningthe kinematic contact condition between the foot or foot part and theground or concerning the dynamics of the movement, and it is possible todetermine in which phase of a stride the patient is located. If there isno linear acceleration or only a very slight linear acceleration, thefoot, by which is also understood a prosthetic foot or a foot part of anorthosis, is still located in the stance phase, of if there is also nolonger any vertical acceleration, the set-down phase is ended, such thatthe linear accelerations can be used to draw conclusions regarding theorientation and positioning of the leg. For example, the accelerationscan be used to determine corresponding speeds, which can likewise besuitably used for the control.

In a development of the invention, provision is made that the reductionof the flexion resistance takes place when there is a hyperextension ofthe below-knee component, i.e. that the hyperextension is one of thoseparameters that are used as controls to change the flexion resistance.The knee angle of 0° is assumed if the below-knee component bearswithout force on an extension stop. An increase in the knee angle isassumed if a bending of the knee joint is performed counter to thewalking direction. If the knee is hyperextended, the knee angledecreases further, since it is regarded as a negative knee angle. If theknee joint experiences an extension moment about the knee axis as aresult of forces acting on the joint, for example via the groundreaction force, stump forces or hip moments, a hyperextension may occurwhich, when detected, can signal that the patient is in the terminalstance phase and, therefore, a swing phase should be enabled.

The knee joint can have an elastic extension stop, for example in orderto prevent the below-knee component from swinging hard against the stopin an extension movement. The elastic extension stop can be composed ofelastomer bodies, spring elements or the like. By virtue of the elasticextension stop, it is possible to permit a hyperextension in a smallangle range when an extension moment is applied about the knee axis,and, when the extension moment ceases, the below-knee component isbrought back by the elastic extension stop to the extended or almostextended position, in which the knee angle is 0°. After the load hasbeen removed, the joint returns to the extended or almost extendedposition. Knowing the spring characteristics of the extension stop andthe negative knee angle, it is possible to calculate a knee momentacting in the extension direction about the knee joint and, when a kneemoment is present in the extension direction, i.e.

when the elastic extension stop is compressed, to reduce the flexionresistance. The knee moment is calculated on the basis of the knee angleand on the knowledge of the spring characteristic, and force measurementsensors or moment sensors are not needed. If there is a knee moment inthe extension direction, this is a further factor for ascertaining inwhich phase of a step the patient is located and whether a swing phasetakes place directly and, accordingly, the flexion resistance should bereduced.

A rotation direction of the below-knee component can be calculated ordetected via a sensor, for example a gyroscope. The flexion resistanceis reduced only if there is a forward rotation of the below-kneecomponent, in order to rule out the possibility of the flexionresistance being undesirably reduced when walking backward.

Acceleration data of the below-knee component can be determined via anacceleration sensor in order to be able to derive or calculate requiredparameters.

After a reduction of the flexion resistance, the latter can be increasedagain, in particular to a stance phase level or to such a high levelthat unwanted bending is not possible or is possible only slowly, if,within a predefined time interval, no bending of the knee joint takesplace, or if, within a flexion angle after bending, a previouslyestablished limit value for a horizontal acceleration is exceeded. Thisserves to increase the stability if a swing phase is discontinued, i.e.if no complete step cycle can be performed.

An illustrative embodiment of the invention is explained in more detailbelow with reference to the figures, in which:

FIG. 1 shows a schematic representation of a prosthetic knee joint;

FIG. 2 shows a schematic representation of an extension stop;

FIG. 3 shows an example of a control sequence, and

FIG. 4 shows a schematic representation of a control concept.

FIG. 1 shows a prosthetic device for patients with a thigh stump andwith no knee joint and lower leg. A prosthesis socket 1, also designatedas the thigh component of the prosthesis or as the thigh socket, servesto receive the stump (not shown). Arranged on the prosthesis socket 1,there is a prosthetic knee joint 2 which, in the present case, isdesigned as a monocentric knee joint, and a below-knee component 3 ismounted so as to pivot about a pivot axis relative to the thigh socket1. A prosthetic foot 4 is arranged at the distal end of the below-kneecomponent 3. The prosthetic device is shown in a terminal stance phase,the prosthetic foot 4 still located on the ground. Arranged inside thebelow-knee component 3 there is a resistance device 5, which offersresistance to bending, i.e. flexion, and the resistance device 5likewise serves for variable adjustment of an extension resistance. Theresistance within the resistance device is changed via an actuatorwhich, for example, opens or closes valves or redirects hydraulic flows.Alternatively, it is likewise possible that the actuator changesrheological properties of the hydraulic fluid in order to change theresistance. Alternative changes to resistance are possible, for examplethe activation of brakes or the conversion of kinetic energy toelectrical energy.

An inertial sensor 31 is arranged on the below-knee component 3 andrecords the absolute angle φ_(US) of the below-knee component. Theinertial sensor 31 measures the absolute angle φ_(US) of the below-kneecomponent 3 with respect to the vertical and can be configured as a 2Dor 3D magnetic field sensor, a 2D or 3D acceleration sensor or as agyroscope. The absolute angle φ_(US) increases as the inclination of thebelow-knee component 3 in the forward walking direction increases, i.e.during a clockwise pivoting about a distal point of contact with theground. Moreover, an acceleration sensor 12 is arranged on thebelow-knee component 3 and can determine a tangential accelerationa_(T), i.e. an acceleration tangential to the pivot radius of thebelow-knee component 3, and a radial acceleration a_(R), i.e. anacceleration in the direction of the distal rotation point of thebelow-knee component 3, of the knee joint 12. With a correspondingsensor, e.g. a 3D acceleration sensor, it is also possible to detect themedial and lateral accelerations in addition or to detect only theseaccelerations.

Finally, a knee angle sensor 11 is provided via which the knee angle φkcan be detected. The knee angle φ_(K) is regarded as increasingpositively in the flexion direction from the prolongation of thelongitudinal extent of the below-knee component 3; the knee angle φ_(K)is 0 when the longitudinal extent of the prosthesis socket 1 is flushwith the axis of the longitudinal extent of the below-knee component 3.A hyperextension is regarded as a negative knee angle φk.

The prosthetic knee joint 2 can have an elastic extension stop, which isshown schematically in FIG. 2. In addition to the schematic thigh socket1 and the schematic below-knee component 3, which are mounted pivotablyon each other about a joint axis, an abutment 10 is arranged on theupper part of the prosthetic knee joint 2. The abutment 10 issubstantially rigid and, in the extended state as shown in FIG. 2, anelastic stop element 30 bears on the rigid abutment 10. A slighthyperextension is permitted by the spring design and, from knowledge ofthe spring rate of the stop element 30, the knee moment acting in theextension direction can be calculated from the knee angle (PK. Ofcourse, it is also possible to arrange the abutment 10 on the below-kneecomponent and to arrange the elastic stop element on the upper part 1.

To control the enablement of a swing phase, several parameters can beused, namely the forward inclination of the below-knee component 3, i.e.a positive below-knee angle φ_(US) of the below-knee component 3, aforward rotation of the lower leg in the walking direction, i.e. anincrease in the absolute angle φ_(US) of the below-knee component 3, anacceleration of the knee joint, in order in particular to determine thestate of movement of the prosthetic foot 4 at the sole level, and theknee angle φ_(K) and a knee angle velocity ω_(K), which can becalculated from the first time derivative of the knee angle φ_(K).

FIG. 3 shows a schematic control sequence. In order to enable a swingphase and to reduce the flexion resistance R of the resistance device 5,the forward inclination is first determined, i.e. the positive absoluteangle φ_(US) of the below-knee component 3 relative to the vertical. Ifthe absolute angle φ_(US) is above a set limit value, for example 5°,the first condition for enablement of the swing phase is met. If, inaddition, a forward rotation in the form of a lower leg angular velocityω_(US) is detected, it can be assumed that the lower leg is in movement;a forward rotation of >10°/s, for example, can be assumed as limitvalue. As soon as these limit values are met or exceeded, a check ismade to ascertain whether the knee angle φ_(K) corresponds to a setlimit value. In the terminal stance phase, which is adopted beforeinitiation of the swing phase, the prosthetic knee joint 2 is situatedin an extended or almost extended position, and a hyperextension caneven occur in the case of an elastic extension stop. If a limit valuefor the knee angle φ_(K), which is <5° and can also assume negativevalues, is not reached, then a further condition for initiating theenablement of a swing phase is met. The knee moment acting in theextension direction can be calculated using the knee angle φ_(K) and theknown data of the spring device in the elastic extension stop.

In the case of a negative knee angle φ_(K), i.e. in the case ofhyperextension, a check is made to ascertain how great the knee anglevelocity ω_(K) is. If the latter is below a limit value, for examplebelow 7°/s, it can be assumed that there is no or only slight kneeflexion and knee dynamic, which is likewise characteristic for aterminal stance phase. If there is no hyperextension, a check is made toascertain whether the negative angular velocity is below a limit value,and the question here is how great is the knee angle velocity in theflexion direction or extension direction. If the determined knee anglevelocities ω_(K) are below the required limit values, the extent of theacceleration a_(F) at sole level is calculated, which is based on therelative position of the acceleration vector with respect to theprosthetic foot 4. If the acceleration a_(F) at sole level is below alimit value, for example below 3 m/s², it is to be assumed that thekinematic contact conditions between the prosthetic foot 4 and theground correspond to those of a terminal stance phase and, consequently,the reduction of the resistance R of the resistance device 5 can beinitiated.

The clear decision between forward heel-toe walking via the prostheticfoot 4, i.e. a forward stride, and a rearward swing-through of theprosthesis under the body, for example in the swing phase of a rearwardstep, all the steps and questions are necessary that follow theestablishment of a forward inclination and forward rotation of thebelow-knee component 3. For this purpose, a hyperextension of theprosthetic knee joint 2 counter to an elastic extension stop 10, 30 or astrongly extending movement at a low knee angle φ_(K) is needed, whichcan be measured by the knee angle sensor 11. In addition, theacceleration sensor 12 determines whether the extension moment about theknee joint is applied statically or dynamically. In particular, thelinear accelerations of the prosthesis at the sole level are calculated.Assuming that the forward inclination, i.e. the positive absolute angleφ_(US), and a forward rotation of the below-knee component are given,case distinctions can be made on the basis of accelerations and kneemoments and, on the basis of these case distinctions, the flexionresistance R is either maintained at a high stance-phase flexion levelor is reduced to a swing-phase level.

If there is an insufficient extension moment or a sufficient flexionmoment about the prosthetic knee joint 1, or if the knee angle velocityω_(K) is either extending or the prosthetic knee joint 2 is inhyperextension, there can be no enablement of the swing phase.

If the prosthetic knee joint experiences an extension moment about theknee axis on account of dynamic forces, for example on account of theinertial forces of the prosthetic foot 4 and of the below-knee component3, a hyperextension in the knee joint or a stretching movement can bemeasured. If the below-knee component 3 thus moves, this situationcorresponds to that of a pendulum, such that there is no enablement of aswing phase.

Enablement of a swing phase accordingly takes place when an extensionmoment about the knee axis is caused by static forces, such as groundreaction force, and stump forces acting on the prosthetic knee joint. Inthis case, a hyperextension or a greatly stretching movement of the kneejoint is measured, but no or only slight acceleration a_(F) at solelevel. Such a situation is characteristic of the terminal stance phase,in which the prosthesis, loaded in the walking direction, rolls heel totoe over the foot. In this situation, the resistance R is reduced.

The characteristic of the elastic hyperextension, in particular thespring characteristic of the elastic extension stop, and the thresholdvalues for the knee angle φ_(K), the knee angle velocity ω_(K) and theadmissible accelerations a_(F) for enablement of a swing phase have tobe chosen such that, on the one hand, a clear distinction can be made asto whether a swing phase is enabled and, on the other hand, also aslight hyperextension is achieved, for example by users with low bodyweight and with small steps and slow walking speeds.

If, for example, within the first 5° of a knee flexion movement afterenablement of the resistance device 5 to a reduced flexion resistance R,an acceleration a_(F) of a magnitude above a defined threshold isestablished, for example by striking against an obstacle, it is possiblefor the flexion resistance R to be immediately switched back to a highlevel of stance-phase flexion damping, in order to avoid unwantedflexion in an emergency.

All of the measured signals of the sensors can be filtered in order tobe able to compensate for measurement inaccuracies. For the accelerationconditions, asymmetrical limit values can be set in order to be able toperform individual adaptation to the respective gait situation andmovement directions.

The proposed control arrangement does not require direct measurement offorces, and it is therefore possible to do without force sensors thatcan in some cases be sensitive and difficult to evaluate. The sensorsused are exclusively knee angle sensors, inertial angle sensors such asgyroscopes, and acceleration sensors. The moments about the knee axis,particularly in the extension direction, can be easily determined withthese sensors, since the parameters of an elastic extension stop aredetected and used as a basis for the calculation.

The easily determinable linear and angular accelerations are used tocalculate the state of movement of the prosthesis, in particular toidentify the state of movement of the prosthetic foot 4. Through thelogical linkage of forces and moments with accelerations, it is possibleto distinguish between static forces and dynamic forces and moments,such that this distinction permits detection of the walking pattern. Inthis way, a distinction can easily be made as to whether a freeswing-through or a terminal stance phase is present.

The control according to the method described moreover also permits thereliable enablement of the swing phase even with slow walking speeds,small strides and on soft ground, for example loose sand or snow. Thecontrol is independent of the patient's weight and is able to ensure thepatient can safely walk backward.

FIG. 4 shows a schematic view of a control concept of a prosthetic kneejoint, the set-up of the prosthesis corresponding to that of FIG. 1. Itis also possible in principle to use the control concept in orthoses,particularly in what is called a KAFO (knee ankle foot orthosis). Theprosthesis socket 1 or the thigh component is connected to thebelow-knee component 3 via the prosthetic knee joint 2. The prostheticfoot 4 is arranged at the distal end of the below-knee component 3. Theresistance device 5 is likewise situated inside the below-knee component3. The elastic extension stop, which can be arranged in particularinside the resistance device 5, is shown on the right next to theschematic representation of the prosthetic device. The prosthetic deviceis located in the extended stride position in the terminal stance phase,which means that, in the front area of the foot, a resting and rotatingpoint 6 is created about which the prosthetic device rotates. On accountof the lever between the longitudinal axis of the below-knee component 3and the resting point 6, an extension moment is applied around the kneejoint 2, and this has the effect that the abutment 10, which in thiscase is movable and part of a hydraulic piston, is pressed against thestop element 30 in the form of a spring. At the same time, it isascertained whether the prosthetic device has a forward inclination,which is indicated by the curved arrow. If an absolute angle φ_(US) ispresent, i.e. an inclination to the vertical in the clockwise directionin the illustrative embodiment shown, and if a forward rotation takesplace, i.e. an increase of the absolute angle φ_(US) in the forwarddirection of walking, wherein the rotation takes place about the distalresting point 6, further criteria are given for determining theinstantaneous state and the phase within a gait cycle or a gaitsequence. The extension moment can be calculated from the spring rate ofthe stop element 30 and the knee angle, in this case the negative kneeangle φ_(K).

To rule out the possibility of the below-knee component simply swingingfreely about the knee joint 2, the linear acceleration a_(F) at thecontact point 6 is determined. If this acceleration is 0 or very low, itcan be assumed that the prosthetic foot 4 and the resting point 6 haveground contact, such that a stationary rotation point is present at theresting point 6. The load is virtually static. In the case of a staticload, a forward inclination and forward rotation and, if appropriate,hyperextension, if the knee moment extension moment does not exceed alimit value X, the flexion resistance R of the resistance device 5 isthen reduced, such that a bending of the prosthetic knee joint 2 caneasily take place.

1. A method for controlling an artificial orthotic or prosthetic kneejoint, on which a below-knee component is arranged and which is assigneda resistance device, the method comprising: determining sensor data viaat least one sensor during use of the orthotic or prosthetic knee joint;changing a flexion resistance R in accordance with the sensor data;determining a linear acceleration a_(F) of the below-knee component;comparing the determined linear acceleration a_(F) with at least onethreshold value; changing the flexion resistance R if the thresholdvalue is reached.
 2. The method as claimed in claim 1, furthercomprising determining an extended stride position of a prosthesis ororthosis having the artificial prosthetic or orthotic knee joint, andreducing the flexion resistance R when the extended stride position ispresent.
 3. The method as claimed in claim 1, further comprisingdetermining an absolute angle φ_(US) of the below-knee component inorder to detect a terminal stance phase, and reducing the flexionresistance R if a predefined limit value for the absolute angle φ_(US)of the below-knee component is exceeded.
 4. The method as claimed inclaim 3, further comprising measuring the absolute angle φ_(US) of thebelow-knee component from an absolute angle of a thigh component and aknee angle φ_(K) or directly with an inertial angle sensor.
 5. Themethod as claimed in claim 1, further comprising determining a kneeangle φ_(K) via a knee angle sensor, and reducing the flexion resistanceR if a predefined limit value for the knee angle φ_(K) is not reached.6. The method as claimed in claim 1, further comprising determining aknee angle velocity ω_(K), and reducing the flexion resistance R onlywhen a limit value is exceeded.
 7. The method as claimed in claim 1,further comprising calculating or detecting an angular velocity ω_(US)of the below-knee component via a sensor, and reducing the flexionresistance R only when the angular velocity ω_(US) is below a limitvalue.
 8. The method as claimed in claim 1, further comprising using thelinear acceleration a_(F) of the below-knee component at the sole levelas a basis for the control.
 9. The method as claimed in claim 1, furthercomprising reducing the reduction of the flexion resistance R when thereis a hyperextension of the below-knee component.
 10. The method asclaimed in claim 1, wherein the knee joint has an elastic extensionstop, the method further comprising: calculating a knee moment iscalculated via the knee angle φ_(K); calculating a spring characteristicof the extension stop; reducing the flexion resistance R if a kneemoment in the extension direction exceeds a threshold value.
 11. Themethod as claimed in claim 1, further comprising calculating ordetecting a rotation direction of the below-knee component via a sensor,and reducing the flexion resistance R only if there is a forwardrotation.
 12. The method as claimed in claim 1, further comprisingdetermining acceleration data of the below-knee component via at leastone of an acceleration sensor and an inertial angle sensor.
 13. Themethod as claimed in claim 1, wherein, after a reduction of the flexionresistance R, the method further comprising increasing the flexionresistance R again if, within a predefined time interval, no bending ofthe knee joint took place, or if, within an enclosed knee angle φ_(K), alimit value for an acceleration is exceeded.
 14. A method forcontrolling an artificial orthotic or prosthetic knee joint, theorthotic or prosthetic knee joint including a resistance device, themethod comprising: providing at least one sensor and a below-kneecomponent positioned on the orthotic or prosthetic knee joint;determining sensor data via the at least one sensor during use of theorthotic or prosthetic knee joint; changing a flexion resistance appliedby the resistance device using the sensor data; determining a linearacceleration of the below-knee component with the sensor data; comparingthe determined linear acceleration with at least one threshold value;changing the flexion resistance if the threshold value is reached. 15.The method as claimed in claim 14, further comprising determining anextended stride position of a prosthesis or orthosis having theartificial prosthetic or orthotic knee joint, and reducing the flexionresistance when the extended stride position is present.
 16. The methodas claimed in claim 14, further comprising determining an absolute angleof the below-knee component in order to detect a terminal stance phase,and reducing the flexion resistance if a predefined limit value for theabsolute angle of the below-knee component is exceeded.
 17. The methodas claimed in claim 16, further comprising measuring the absolute angleof the below-knee component from an absolute angle of a thigh componentand a knee angle or directly with an inertial angle sensor.
 18. Themethod as claimed in claim 14, further comprising determining a kneeangle via the at least one sensor, and reducing the flexion resistanceif a predefined limit value for the knee angle is not reached.
 19. Themethod as claimed in claim 14, further comprising determining a kneeangle velocity, and reducing the flexion resistance only when a limitvalue is exceeded.
 20. The method as claimed in claim 14, furthercomprising calculating or detecting an angular velocity of thebelow-knee component via the at least one sensor, and reducing theflexion resistance only when the angular velocity is below a limitvalue.